This invention relates to heating systems of the forced air type and more particularly to a fireplace type heat exchange unit adapted for connection into the ducts of a forced air heating system.
Conventional fireplaces having an open hearth are extremely inefficient sources of heat for the room or building within which they are located. Typically, up to 90% of the heat generated by the burning material in the fireplace is lost up the chimney. Only 10% of the heat generated by the burning material radiates out of the fireplace to heat the room. Further, such open hearth fireplaces create a draft which in fact will cool down other rooms in the house as air is drawn or infiltrates from the exterior of the house and from the other rooms to the fireplace to support combustion. With such conventional fireplaces, drafts of 100-250 CFM are typical. This flow of air passing into the open fireplace and up the chimney is substantially more than is required to support combustion.
Various proposals have been made to increase the efficiency of fireplaces so that they may supplement the existing home heating systems or to at least reduce the negative effect of a fireplace on the overall efficiency of the home heating system. For example, it has been proposed to close the fireplace opening with high temperature, heat resistance glass doors. Such doors reduce the amount of heat loss up the chimney. These doors, however, alone do not substantially increase the overall heating efficiency of the fireplace.
With systems designed to supplement existing heating systems, a firebox is typically placed within a steel enclosure or within a fire brick or masonry enclosure so as to define with the enclosure a heat exchange space. Cold air inlets are provided at the floor level adjacent the fireplace and hot air outlets are positioned above and/or to the sides of the fireplace. The combustion gases within the firebox will heat the enclosure and the firebox. Natural convection draws cold air into the inlets through the enclosure, past the firebox, out the outlets and into the room within which the fireplace is placed. Although increasing the heating efficiency when compared to conventional fireplaces, such arrangements are incapable of heating the entire home or building within which the fireplace is located. Examples of such prior fireplace type heat exchange systems may be found in U.S. Pat. No. 1,670,034 to Halberg, entitled FIREPLACE and issued on May 15, 1928; U.S. Pat. No. 3,965,886 to Nelson entitled HOME FIREPLACE HEATING and issued on June 29, 1976; and U.S. Pat. No. 3,998,203 to Jensen entitled AIR HEATER FOR FIREPLACES and issued on Dec. 21, 1976.
In an attempt to increase the overall heating efficiency of fireplace units and to provide heat to rooms other than the room within which the fireplace is located, it has been proposed to position the fireplace heat exchange unit in line with the cold air return ducts or in line with the hot air distribution ducts of a conventional heating system. Examples of these forms of home heating systems including such supplemental fireplace heat exchangers may be found in U.S. Pat. No. 2,186,539 to Slayter et al, entitled HEATING SYSTEM and issued on Jan. 9, 1940; U.S. Pat. No. 2,191,064 to Wagner, entitled HEATING APPARATUS, and issued on Feb. 20, 1940; U.S. Pat. No. 2,231,258 to Elmore entitled HEATING SYSTEM and issued on Feb. 11, 1941; U.S. Pat. No. 2,333,146 to Beyer, entitled HEATING AND VENTILATING FIREPLACE SYSTEM, and issued on Nov. 2, 1943; and U.S. Pat. No. 4,004,731 to Zong, entitled DEVICE FOR TRANSFERRING HEAT ENERGY FROM A FIREPLACE TO A FLUID HEATING SYSTEM and issued on Jan. 25, 1977.
Although systems of the type disclosed in the aforementioned U.S. Patents do increase the heating efficiency of fireplaces and do circulate some of the heat which is typically lost up the chimney, these systems are incapable of providing sufficient heat to serve as the sole means for heating average size dwellings within which they may be located.